Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $33.63   8.201%   $36.388   $36.39   $36.40   $36.40  
  Purchase #2 $57.31   7.205%   $61.4392   $61.44   $61.45   $61.40  
  Purchase #3 $191.39   8.497%   $207.6524   $207.65   $207.65   $207.70  
  Purchase #4 $153.83   3.717%   $159.5479   $159.55   $159.55   $159.50  
  Purchase #5 $219.78   11.451%   $244.947   $244.95   $244.95   $244.90  
  Purchase #6 $249.39   12.251%   $279.9428   $279.94   $279.95   $279.90  
  Purchase #7 $30.51   13.767%   $34.7103   $34.71   $34.70   $34.70  
  7 purchase totals = $935.84       $1,024.6276   $1,024.63   $1,024.65   $1,024.50